The present invention relates to valves used in oil wells. More particularly, the invention relates to a safety valve used in connection with a slip joint in a testing string for testing submerged oil well formations.
When testing submerged oil wells from vessels, a slip joint is normally installed above the packers to compensate for wave action. The slip joint is normally placed in the string far enough above an oil well testing packer so that a constant weight of the pipe in the testing string is allowed for expansion of the packer while the slip joint is in motion due to wave action.
The drill pipe above the slip joint is in tension and is normally supported by a hang-off point formed by a built-in upset on the pipe being supported by a corresponding pipe hanger in a subsea test tree normally installed in the ocean floor. After the testing packer is set and the drill string is supported by the hang-off point, it can be seen that if the testing string parts below the hang-off point that the testing string may collapse into the well bore with little or no immediate indication at the surface of the sea on the vessel.
The present invention is a safety valve that is normally placed above the slip joint in that part of the testing string in tension. If the testing string does separate below the hang-off point, the safety valve will close the interior of the testing string after the slip joint is fully collapsed and the safety valve is placed in compression.
A slip joint is disclosed in U.S. Pat. No. 3,646,995 to Manes et al issued Mar. 7, 1972 wherein a stinger is included in the slip joint. At the end of the slip joint is a cap in which the stinger seats when the slip joint is fully collapsed to shut off flow through the apparatus. This slip joint, as illustrated in FIG. 3a, does not provide a full opening through the testing apparatus.
Tester valves such as that shown in U.S. Pat. No. 3,435,897 to Barrington issued Apr. 1, 1969 and U.S. Pat. No. 3,814,182 issued to Giroux June 4, 1974 disclose full opening tester valves for placement immediately above a packer wherein a ball valve in the tester valve is rotated to the full opening position when sufficient weight is exerted on the tester valve to operate the mechanism.
A safety valve apparatus disclosed in U.S. Pat. No. 3,351,133 to Clark, Jr. et al issued Nov. 7, 1967 discloses an oil well production safety valve which provides a full opening ball rotatable to the closed position if production pressure is lost and downward weight is thereby directed to the apparatus of the rotatable ball valve.
The present invention includes a ball valve which is held in the normally open position by a spring means. This means biases the valve to the open position to assure that the slip joint normally placed below the safety valve is fully collapsed before the compression placed on either end of the safety valve acts to close the safety valve. Also, a pressure piston is included in the apparatus which, responsive to the pressure differential between the pressure in the well annulus exterior of the tool and the pressure in the center bore of the tool, assists in maintaining the ball in the open position.
The ball opening mechanism includes a bypass means whereby fluid pressure is bypassed around the ball when the ball is being opened from the closed position, to balance the pressure in the bore below the ball with the pressure in the bore above the ball. Also, spring means is provided in the tool to apply an opening force to the rotatable ball such that when a pressure differential across the ball is lowered to the point that the ball may rotate, the ball is quickly rotated to the open position under the influence of the spring means. This spring means prevents an overstress from being applied to the ball rotating pins of the apparatus to prevent these pins from being separated from the ball operating mechanisms of the invention.
Also disclosed is an alternate configuration of the bypass means so that the apparatus of the present invention may be easily converted into a tester valve.